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The pincushion cactus, Escobaria vivipara(Nutt.) Buxb., is a wide-ranging variable species occurring from Canada to Mexico, and found throughout New Mexico below about 2,600 metres (8,500 ft). Nine varieties have been described. Where the varieties of the pincushion cactus meet, they intergrade. The variety Escobaria vivipara var. arizonica is from Arizona, while Escobaria vivipara var. neo-mexicana is from New Mexico.

The term is defined in different ways by different authors.[3] However, the International Code of Nomenclature for Cultivated Plants, while recognizing that the word "variety" is often used to denote "cultivar", does not accept this usage. Variety is defined in the code as follows: "Variety (varietas) the category in the botanical nomenclatural hierarchy between species and form (forma)". However the code acknowledges the other usage as follows: "term used in some national and international legislation for a clearly distinguishable taxon below the rank of species; generally, in legislative texts, a term equivalent to cultivar. See also: cultivar and variety (varietas)".[4]

A variety will have an appearance distinct from other varieties, but will hybridize freely with those other varieties (if brought into contact).[5]

In plant breeding nomenclature, at least in countries that are signatory to the UPOV Convention, "variety" or "plant variety" is a legal term.

In zoological nomenclature, the only allowed rank below that of species is that of subspecies. A name that was published before 1961 as that of a variety is taken to be the name of a subspecies. A name published after 1960 as that of a variety does not formally exist. In zoology, forms and morphs are used informally if needed, but are unregulated by the ICZN.

In bacteriological nomenclature, "variety" is not allowed, but names published as varieties before 1992 are taken to be published as subspecies.

^"Article 4". International Code of Nomenclature for algae, fungi, and plants. 2012. 4.1. If a greater number of ranks of taxa is desired, [...a]n organism may thus be assigned to taxa of the following ranks (in descending sequence): [... genus, ... species, subspecies,] variety (varietas), subvariety (subvarietas), form (forma), and subform (subforma). ... 4.3. Further ranks may also be intercalated or added, provided that confusion or error is not thereby introduced.